ctrl-keys are inactive since 4.1.16

Description

Both ctrl-keys (left and right) are inactive since the update to 4.1.16,
host is Ubuntu 10.04 LTS, guest ist Win 2000 SP4.

This means that I cannot use ctrl-p for printing, ctrl-f for searching etc. The keyboard ist not defective, since all is well on the host system. I have tested two hosts (both Ubuntu 10.04) an several guests (all Win 2000 SP 4 with different VirtualBox settings.